The present invention generally relates to centrifuge rotors, and is more specifically directed to the mechanism whereby rotor parts are coupled together.
The present invention concerns a locking ring for joining a first and a second part of a rotor in a centrifugal separator, which rotor is arranged to rotate around a rotational axis and delimits within itself a separation chamber. The first rotor part has a circular cylindrical end portion, which has an inner radius and a center line, which coincides with the rotational axis. The second part has an annular flange portion, which extends around the rotational axis in a plane perpendicular to the rotational axis. The flange portion has an outer radius, which is approximately as large as the inner radius of the circular cylindrical end portion, the flange portion being insertable in the end portion of the first part in one axial direction against a stop arranged in the rotor and is adapted to be lockable in the opposite axial direction by means of a locking joint comprising the locking ring. When assembling the rotor, the locking ring is arranged to be brought radially outwardly from a position radially inside the inside of the circular cylindrical end portion and axially outside the annular flange portion into a recess extending around the rotational axis in the inside of the circular cylindrical end portion with a certain outer radius so that a radial outer portion of the locking ring extends out into a recess, whereas a remaining radial inner portion of the locking ring extends radially inside the outer radius of the flange portion and so that the outer portion of the locking ring abuts against the circular cylindrical end portion via two radially outer identical contact surfaces and so that the inner portion of the locking ring abuts against the flange portion via two radially inner identical contact surfaces. The contact surfaces are essentially rotationally symmetrical around the rotational axis and are adapted to transfer the axial forces due to the liquid pressure in the separation chamber on the second rotor part to the first rotor part.
Rotor parts of centrifugal separators are often joined together by means of screw joints, in which a big locking ring having an external thread surrounding the rotational axis is screw tight in an internal thread of a circular cylindrical portion of the one rotor part.
Above all, locking joints of this kind cause high manufacturing costs, as well as assembling and disassembling costs. Besides, these joints are exposed to heavy loads, which lays high demands on dimensioning, choice of material etc. It might even happen that the material in the threads is exposed to such high loads that the threads seize during assembly when a certain pre-load is being established.
In U.S. Pat. No. 4,710,160 another locking joint is disclosed. In this locking joint two or more locking rings are brought radially out into an internal groove in a circular cylindrical portion of one rotor part. The disclosed locking ring is fixed in the groove and is pre-loaded by means of tightening rings in a mating rotor part.
By this method, a locking joint is accomplished, which reduces the disadvantages mentioned above. However, the locking joint comprises several components, which must be manufactured, assembled, and occasionally be disassembled and re-assembled. Consequently, this locking joint causes high manufacturing costs and handling costs.
The object of the present invention is to accomplish a locking, by means of which these disadvantages are further reduced without jeopardizing the safety of the locking joint.
According to the present invention this is accomplished by the fact that the locking ring extends substantially a complete revolution around the rotational axis with two end surfaces turned towards one another in the circumferential direction and being so formed in one single integrated piece out of an elastically resilient material that it, in the unloaded condition tends to be substantially annular shaped with an outer radius, which is at least as large as the outer radius of the recess. The contact surfaces are located and directed so that in every axial section around the rotational axis there is a middle point, in which the contact surfaces have a direction of normalcy. This middle point is common and coinciding for all the contact surfaces, and in a direction towards the separation chamber in the interior of the rotor forming an acute angle with the rotational axis. The contact surfaces are substantially symmetrical with respect to this direction of normalcy.
Thereby, the resulting force on the locking ring from the first rotor part and the resulting force of equal strength but counter directed from the other rotor part become located just opposite one another in every axial section around the rotational axis, resulting in the locking ring not being exposed to any forces that tend to bring the locking ring out of the recess.
In a preferred embodiment all the contact surfaces are parallel and conical. Preferable the locking ring has a retangular cross-section.
In another embodiment of the invention, the locking ring has such an extension (1) in the circumferential direction and such a radial thickness (t) that the distance in the circumferential direction between the end surfaces in mounted state is less than 3.14 t.
In a variation of this embodiment, the locking ring has such an extension in the circumferential direction and such a radial thickness (t) that the distance in the circumferential direction between the end surfaces in mounted state is less than 1.5 t.